Penetration method op road construction



Reissued Nov. 15, 1932 UNITED STATES 1 EDWIN C.WALLAOE, OF WEST NEWTON, MASSAOHUSETTS, ASSIGNOR TO WARREN BROTHERS COMPANY, OF CAMBRIDGE, MASSACHUSETTS, A CORPORATION OF NESTv VIRGINIA.

No Drawing. Orig'inal No. 1,740,718, dated December 24, 1929, Serial No. 300,958, filed August 20, 1928.

PENETRATION METHOD 01 ROAD CONSTRUCTION Application for'reissue filed November 30, 1931. Serial No. 578,194;

For some years past, highways, streets and roads have been constructed under the term bituminous macadam penetration method by spreading crushed stone, gravel or slag upon a previously prepared base in a layer from 2-6" or more in thickness which is determined by trafiic conditions, then applying thereto, generally by spraying under pres- 4 ,sure, a rather soft bituminous cementing me- 1 dium in ahighly heated condition.

A thin la er of smaller stone is then spread over this bituminous coating and rolled. More heated bituminous ,cement is then applied and after covering it with stone screenings, sand or similar material, the entire mass is thoroughly compacted.

Some roads constructed by this method have given excellent results, but others constructed by the samemethod under similar conditions have been very troublesome, ex pensive to maintain and generally unsatisfactory. In order to cause proper adhesion of the bituminous cement to the stone, it is the n general practice in Work of this type to use bituminous cement of rather soft consistency. When tested at C. (77 F.) a No. 2 needle weighted to 100 grams will sink from-1O to.

15 mm. in 5 seconds. This is usually referred penetration machines now in general use.

When exposed to the rays of the summer sun this bituminous cement softens and by coming to thee-surface, causes the condition technically known as bleeding.

harder consistency than could otherwise be used and also by reduction of the amount required to waterproof the surface and bond to as 100 to 150 penetration on standard Wherever bleeding occurs it is necessary the stone firmly together so there is no excess bitumen to be forced to the top under the condition which usually causes bleeding.

By this method it is possible to use bituminous cement of a consistency from 10 to .harder. and to reduce the quantity required from 5 to 20% below the normal requirements of the usual method of construction.

It also obviates difficulties caused by fine dust adhering to the stone, a condition which it is practically impossible to avoid as dust is I formed by attrition of the stone during process of rolling and even when perfectly clean at time of spreading there is more or less adherent-dust by thetime the bituminous cement is applied.

The improved process may be described as follows:

Upon the previously prepared base, a layer of stone-of the desired size is spread to such depth that after thorough compression the layer will be of required thickness, say 2 to 4 inches, although the thickness of the layer may be any desired depth. y

The stone is coated either before or after it is in place, with a small quantity of hydro- Y adhere'firmly to the stone, notwithstanding I the presence of hygroscopic moistureand adherent particles of dust which can never be wholly eliminated. While it increases the adhesion between the stone and the cement the oil does not soften the bituminous cement to anappreciable degree.

It must be miscible in all proportions with the bituminous cementing medium and preferably consists of'a mixture of cyclic and open chain hydrocarbons with specific gravity ranging from .8 to .92 and volatility not exceeding one third of its volume in five hours at 100 C. (212 F.), with viscosity in the Engler viscosimeter at 25 C. ranging betweeii'75 and 135 seconds.

'It is preferably applied to the stone at least two hours before the application of the J i v t I i bituminous cementing medium in order to F allow all 'portions of the surface of the stone pieces to be thoroughly wetted by the oil without using an excess.

Whether the stone is coated before or after it is in place upon the road, under average working,- conditions, one (1) gallon of oil should cbv'er sufficient stone to form a layer 3" thick after compression over an area of 8 to 10 sq. y ds.

After stone is in place it is compacted until a loaded truck may be driven over it without displacing the stone to form ridges or rats. It is then coated with heated bituminous ce- 'ment at the rate of 10 to lbs. per sq. yd; 12.5 lbs. or approximately 1 gal of heated bituminous cement applied to the oil coated stone will bind the particles as firmly together as the 15, or more pounds per sq. yd. usually required for stone not previously coated with oil.

After the application of the bituminous cement a second layer of stone substantially free from' dust or excessively fine material is spread. It is smaller sized pieces of stone than that used in the first layer and it is spread in a thinner layer, using sufficient to cover the underlying layer with little or no excess. It is good practice for'this layer to use stone substantially all of which passes a screen on which the stone used in the first layer is retained. For instance. if stone in the first layer is retained on 1 screen, and

for use in the second layer, it should pass 1%" screen and be retained on A" screen. I' prefer, however, to use stone in the first layer which passes 2 and is retained on 1? screen and for the second layer use stone passing 1" and retainedon The oil'coating of this second layer, must either be omitted or applied to the stone of this layer before it is spread. It is preferable to use 'for this layer, stone which has been coated with oil several hours before it is spread in place, but the oil coating may' be omitted without departing from the spirit of the invention, as the chief consideration. is the oil coating applied to the stone which forms the body ofthe pavement. v

After the second or intermediate layer of stone has been spread, it is compacted with heavy roller until firmly seated on;the underlying layer and then it is in turn coated with 'theheated bituminous cement. using from 20 to of the quantity applied to the first layer, and afterwards covered with. fine stone,

coarse sand or grit which by preference has been. coated with oil some time previous to itsuse.

In some cases it has been found advisable tospread or broadcast over the lower layer after the application of the bituminous cement, but before spreading the intermediate layer of stone, a thinlayer of coarse sand, preferably coated with oil which is spread at the rate of approximatelylfi to 30 lbs. per sql yd. Then after spreading the intermediate course of stone and rolling until firmly seated in place, coating it with the bituminous cement as described above.

Although the use of oil-coated stone for the intermediate and finishing layer is not essential to my process, I prefer to use it wherever a superior product is desired.

After the finishing course of fine. stone, stone grit, fine gravel or sand is spread, it is preferable to roll the surface to force the top coat into the interstices of-the intermediate course of stone andbind the two layers togeth-er. traffic without rolling, provided the fine material thrown to the sides of the street by passing vehicles is replaced until sufiicient has been bonded to the surface by traffic to effectively seal the surface to the action of the elements.

In some instances the coating of bituminous cement upon the intermediate layer of stone and the top dressing of fine stone or grit will be dispensed with and in lieu thereof using a mixture of bitumen and mineral aggregate which may be spread to any desired depth from to 2" according to traflio conditions,

then firmly compacting it in place. Where this is done it is advisable to use slightly smaller stone for the intermediate layer, preferably stone passing screen and retained on 8 to 19 mesh, using sufficient to thoroughly cover without appreciable excess the bituminous coating upon the underlying layer of coarse stone.

The same size stone may be used as for the It may, however, be thrown open tointermediatelayer and a very thin dressing is applied to the layer of stone, it not only adheres' more strongly to the surfaces of the pieces-of stone, but also flows more readily over the same and will flow through smaller openings between the stones than'if unoiled stone had been used. the result being that a for greater proportion of the total'surfaces v invention is that when the bituminous cement of all the stone particles which lie below the surface of the layer are coated with bituminous cement than if the oil had not been used.

theory is that this phenomenon is due to a reduction of the surface tension of the bituminous cement where it 'comes into contact with the oil treated stone surfaces.

Having thus described the invention, what is cla med as new is 1. The method of surfacing. roads which consists in providing, upon a previously prepared foundation, a course of oil-coated stone, and, thereafter prior to its ultimate compression, applying to said course, in situ a coating of bituminous cement.

2. The method of surfacing roads which consists in providing, upon a previously prepared foundation, a course of oil-coated stone, and, thereafter prior to its ultimate compression, applying to said course, in situ a coating of bituminous cement, the oil applied to the stone being limited to such quantity as is required to coatthe stone surfaces and soften the bitumen immediately adjacent the same without materially softening the body of the.

bitumen. Y

3. The method of surfacing roads which consists in providing, upon a previously prepared foundation, a course of oil-coated stone and, thereafter prior to its ultimate compres sion, applying to said course, in situ a coating of bituminous cement, the oil applied to the stone being substantially non-volatile at atmospheric temperatures and being limited to a quantity sufiicient to coat the stone sur faces and soften the bitumen immediately adjacent the same without materially softening the body of the bitumen.

4. The method of surfacing roads which consists in providing upon a previously prepared foundation a course of oil-coated stone and, thereafter prior to its ultimate compression, applying to said course, in situ a coating of bituminous cement of penetration less than 100 at 77 F,-, the oil applied to the stone being limited to a quantity sufficient to coat the stone surface and soften the bitumen immediately adjacent the same without materially softening the body of the bitumen.

5. The method of surfacing roads which consists of providing upon a previously prepared foundation, a course of oil-coated stone and prior to its ultimate compression apply ing thereover a coating of heated bituminous composition, then spreading thereon a relatively thin, intermediate course of oil-coated stone particles which are approximately onehalf to one-quarter the size of the stone particles comprising the lower course and after partial compression spraying the surface with heated bituminous composition, then applying thereover a finishing course of oilcoated fine mineral matter. 7

6. The method. of surfacing roads which consists in providing upon a previously prepared foundation a layerjof oil-coated stone then prior to its ultimate compaction, applying a coating of heated bituminous cement at the rate of approximately 8 to 20 lbs. per sq. yd., then spreading thereover a relatively thin, intermediate layer of dry uncoated stone, the particles of which are approximately one half to one quarter the size of the stone particles, comprising the lower'layer and after applying a coat of the heated bituminous cement approximately 20 to 40% of at the rate of 8 to 20 lbs. per sq. yd., then' spreading thereover a relatively thin layer of small stones, compressing it and applying thereto'a heated bituminous cement at the rate of 2 to 8 lbs. per s yd., and thereafter applying a thin layer of grit, coarse stone, or fine gravel, compacting the mass until it be comes unyielding under the action of the roller.

8. A method of surfacing roads which consists in providing .upon a previously prepared foundation a layer of oil-coated stone, compacting it until firmly seated in place then applying thereover heated bituminous cement sufficient in quantity to bond the stone firmly together and covering this with a thin layer of small stone substantially free from fine material which is firmly seated upon the underlying layer by compaction and finally covering the surface to any desired depth from to 2""with a mixture of bitumen and mineral aggregate and compacting the mass until it becomes unyielding under the action of'the roller.

9. The method of surfacing roads which consists of providing upon a previously prepared foundation a course of oil coated stone and prior to its ultimate compression applying thereover a coating of heated bituminous composition, then spreading thereon a relatively thin, intermediate course of oil-coated stone particles which are substantially smaller than the size of the stone particles comprising the lower course and after partial compression spraying the surface with heated bituminous composition then applying thereover a finishing course of oil-coated fine mineral matter, the oil used in such layers being a substantially non-volatile mobile oil.

10. A process of making a road from five essential materials, namely: (a) coarse stone, (Z1) finer stone, (0') fine gritty mineral matter, (65) a substantially non-volatile oil, and (e) a bituminous cement, which comprises (A) forming a layer of the coarse stone the pieces of which are coated with a substantially non-volatile mobile oil, and coating the same with hot bituminous cement; (B) formin g thereon a second layer of the finer stone the pieces of which are coated with a substantially non-volatile mobile oil and coating the same with hot bituminous cement,'and

C a plyin a to coatin of the fine itty lin er-1 matt er, sa fd steps A, B and C eing performed in the order stated, but the sequence of the steps of coating the stone with oil and spreading it in layers being changeable at W111.

In testimony whereof I afiix my signature.

EDWIN G. WALLACE. 

